Browsing by Author "Kühlwein, Jürgen"
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Item Open Access 2-Isocyanato-2-alkenoates : synthesis and reactions(1989) Effenberger, Franz; Baumgartner, Christian; Kühlwein, Jürgen-Item Open Access 2-Isocyanato-2-alkensäureester : Synthese und Reaktionen(1989) Effenberger, Franz; Baumgartner, Christian; Kühlwein, JürgenZwar erwünscht, aber doch überraschend, waren die Ergebnisse, die wir jetzt mit Phosgen und Diphosgen als "Acylierungsmittel" in dieser Zersetzungsreaktion fanden. Als Reaktionsprodukte wurden in sehr guten Ausbeuten die 2-Isocyanato-2-alkensäureester 2 erhalten.Item Open Access Darstellung und Reaktionen von 2-Isocyanato-2-alkensäureestern (Aminosäuren ; 18)(1994) Effenberger, Franz; Kühlwein, Jürgen; Baumgartner, Christian2-Isocyanato-2-alkenoates 3 were obtained in good yields by the perrhenate-catalyzed decomposition of 2-azidoalkanoates 1 in the presence of diphosgene (2a) or phosgene (2b). Methyl 2-azidopropionate (1h) reacts to give a mixture of methyl 2-isocyanato-2-propenoate (3h) and methyl 2-chloro-2-isocyanatopropionate (4). The addition product 4 could easily be converted into 3h by elimination of HCl with triethylamine at 0°C. With benzyl alcohol (5a) and tert-butyl alcohol (5b) the isocyanates 3 react smoothly to give the corresponding Z- or Boc-protected 2,3-didehydroamino acid esters 6 and 7, respectively. The acrylic acid derivative 3h reacts as dienophile with various dienes to yield the Diels-Alder adducts 8-10.Item Open Access Darstellung von N-Acyl-2,3-didehydro-2-aminocarbonsäureestern (Aminosäuren ; 16)(1993) Effenberger, Franz; Kühlwein, Jürgen; Drauz, Karl-HeinzN-Acyl-2,3-didehydro-2-amino acid esters 3, 5, 7-12, with a great variety of N-substituents, are obtained in good yields by the perrhenate-catalyzed decomposition of methyl 2-azido carboxylates 1 in organic solvents in the presence of the corresponding acyl chlorides 2. By using methyl 2-azidoisovalerate (1a), the conditions (catalyst, solvent, temperature) for the reaction to give 3a were optimized. The reactivity of acyl chlorides can be strongly enhanced with equimolar amounts of dimethyl formamide, which allows a lowering of the decomposition temperature for this reaction. Under these mild reaction conditions also the unstable N-acyldehydroalanine derivative 5f can be obtained in good yield.Item Open Access Eine einfache Synthese von N-Carboxy-α,β-didehydro-α-aminosäure-anhydriden (4-Alkyliden-2,5-oxazolidindionen) (Aminosäuren ; 10)(1988) Effenberger, Franz; Niesert, Claus-Peter; Kühlwein, Jürgen; Ziegler, Thomasα-Azidocarboxylic acids 1 react with phosgene in the presence of catalytic amounts of sodium perrhenate in dimethoxyethane at 85°C to give N-carboxy-α,β-didehydroamino acid anhydrides (4-alkylidene-2.5-oxazolidinediones) 2 in good yields.Item Open Access Eine neue Synthese von Didehydrodipeptiden und Didehydrotripeptiden (Aminosäuren ; 17)(1993) Effenberger, Franz; Kühlwein, Jürgen; Hopf, Martin; Stelzer, UweEsters of N-phthaloyl-protected (R)- or (S)-didehydro dipeptides 5-7 were obtained in good yields by the perrhenate-catalyzed decomposition of 2-azidocarboxylates 1 with N-phthaloyl-protected (R)- or (S)-amino acid chlorides 2 in presence of at least equimolar amounts of N-methyl-2-pyridone (4) as acylation catalyst. Esters of didehydro tripeptides 16 were obtained in a comparable procedure from the optically active amino acid chlorides 2 and 2-(2-azidoacyl)amino acid esters 15, which were prepared from 2-azidocarboxylic acids 12 or the corresponding chlorides 13 with 2-amino acid ester hydrochlorides (S)-14. - As an example, the unprotected (S)-alanly-didehydrovalin 20 was prepared from the didehydro dipeptide 18a without any racemization by hydrolysis of the benzyl ester and subsequent hydrogenolytic removal of the N-phthaloyl group.